The present invention is directed to an improved method and apparatus for removing oil from water or water from oil.
Water and oil frequently get mixed together in various industrial processes or operations. Oil is typically used to lubricate, to fuel, and to provide rust protection. Water is typically used to convey, to dilute, and to wash. The result is that these two liquids frequently get intermingled. Before either can be transported to waste, or be reused, or be used for other less selective operations, they must be separated.
Ship bilge water normally contains substantial quantities of oil. In the past, bilge water was merely pumped overboard, but due to recent environmental controls, it is required that the oil be separated from the bilge water before the water is discharged. Specifically, in order to obtain U.S. Coast Guard approval of oil/water separation units aboard ships, for removing oil from bilge water, it is necessary that the effluent from the unit be less than 15 ppm oil in the water. Although various types of oil separating units have been used in the past to separate oil from bilge water, none of them have consistently produced the results required by the U.S. Coast Guard. Such heretofore known units have included the following:
1. API gravity separators; PA1 2. Parallel plate separators; PA1 3. Parallel plate separators followed by coalescing filters; PA1 4. Chemical settling where flocculants or polyelectrolytes are used; PA1 5. Electrical charge systems; and PA1 6. Air floatation.
All of these types of units do not perform consistently and produce water effluents sufficiently free of oil sheen or oil sufficiently free of water droplets. These units further require extensive attention to control in order to produce the best possible results.
An example of a process and apparatus for separating oil from water is disclosed in U.S. Pat. No. 4,315,822. The system disclosed in this patent discloses the pumping of the oil contaminated water by a low emulsifying pump from the bilge to an oil gravity separator. As the oil and water mixture flows into the separator, the large oil droplets rise to the top of the separator vessel. After this initial separation, the water flows through a plurality of inclined parallel plates in the separator vessel to facilitate the separation of the oil droplets from the water. The water, after gravity separation of the oil, is pumped to a regenerative filter, which is composed of a plurality of superimposed layers of granular media. After removal of oil in the regenerative filter, the water flows through an oil content monitor and then is pumped overboard. If the oil level in the clarified water exceeds a given value, such as 15 ppm, the monitor activates a valve to recycle the water back to the system inlet. This final step is necessary due to the fact that the system disclosed in this patent can not consistently achieve the necessary effluent values.